Scientific knowledge is of two types: knowledge of the properties of physical objects, like the size and mass of a raindrop, and knowledge of what we call “laws of nature.” One of the first human beings to formulate a law of the physical world was Archimedes, more than two thousand years ago. Archimedes “law of floating bodies”:

Any solid lighter than a fluid will, if placed in the fluid, be so far immersed that the weight of the solid will be equal to the weight of the fluid displaced.

We can speculate on how Archimedes arrived at his law. At the time, balance scales were available for weighing goods in the market. The scientist could have first weighed an object, then placed it in a rectangular container of water and measured the rise in height of the water. The area of the container multiplied by the height of the rise would give the volume of water displaced.

Finally, that volume of water could be placed in another container and weighed. Undoubtedly, Archimedes would have performed this exercise many times with different objects before devising the law. He probably also performed the experiment with other liquids, like mercury, to discover the generality of the law. 

All laws of the physical world are like Archimedes’ law. They are precise. They are quantitative. And they are general, applying to a large range of phenomena. Most importantly, all laws of nature discovered by scientists are considered provisional. They are considered to be approximations to deeper laws. They are constantly being revised as new experimental evidence is found or new (and testable) ideas are proposed. 

It is in the process of revision that we see the strongest differences between the methods and beliefs of science and religion.

Knowledge and believing

Everything that we know about the physical world – the domain of science – is subject to revision. Everything must be tested and proved. The knowledge of religion, coming from either the divine authority of the sacred books or from the irrefutable personal transcendent experience, is not subject to revision. It is not an approximation. It is certain. And it cannot be proved. It must be taken on faith.

Paradoxically, all of the knowledge of religion is considered certain, and all of the knowledge of science is considered uncertain. Still, science has done pretty well with its uncertainties and approximations. The approximations of science have been good enough to give us antibiotics and smart phones and rocket ships that can land men on the moon.

Science demands proof for what it believes, even though those beliefs are constantly changing as new experimental evidence becomes available. There is something that scientists believe in that cannot be proven. It is a principle I call the Central Doctrine of Science: The physical world is lawful. All properties and events in the physical universe are governed by laws, and those laws hold true at every time and place in the universe. Graduate students in science absorb this belief through every pore of their skin. It is an unconscious but powerful commitment.

I call the Central Doctrine of Science a doctrine because, despite its success in the past, it cannot be proved. It must be accepted as a matter of faith. No matter how lawful and logical the material cosmos has been up to now, we cannot be sure that something illogical, unexplainable, and fundamentally unlawful might happen tomorrow. Our faith in the Doctrine is so strong that when we find physical phenomena that cannot be explained in terms of current laws, we attempt to revise those laws rather than abandon our belief in a lawful universe.

When it was found in the 19th Century that the orbit of Mercury could not be completely explained in terms of Newton’s law of gravity, scientists did not attribute the discrepancy to an unsolvable mystery or to the breakdown of order in the physical world or to the intervention of a whimsical god. Instead, they recognized a physical problem that required a more advanced physical understanding.

That more advanced understanding was provided by Einstein’s theory of gravity. In fact, I cannot imagine any event in the material world that would cause most scientists to label the event a miracle, unexplainable by science. If a wheelbarrow began to float, a scientist would look for magnetic levitators or, if necessary, assign the phenomenon to some new kind of force. But a natural and lawful force, not a supernatural force. 

So, perhaps I am a person of faith after all. I will have to share this discovery with Micah.

Memphis native Alan Lightman is a physicist, novelist and professor of the practice of the humanities at the Massachusetts Institute of Technology. His new book, “Searching for Stars on and Island in Maine” is published by Pantheon.